1. Field of the Invention
Present invention relates to semiconductor devices and manufacturing methods thereof, in particular, relates to thin and small resin encapsulated semiconductor devices suitable for portable devices such as cellular phones and video cameras, and manufacturing methods thereof.
2. Description of Related Art
Recently, as thin and small semiconductor devices, chip size packages (CSP) of which the external form are formed in conformity with the size of a semiconductor element (semiconductor chip) have been developed. Among them, a fine pitch area package, the pitch between terminals of which is narrow, is seen as a promising candidate.
A thin area package of fine pitch is broadly divided into one that employs an insulating resin film as a matrix, and the other one that employs a resin impregnated glass cloth substrate of rigid frame as a matrix. In particular, from a reliability point of view, the use of the latter one is being studied.
However, in the CSP in which a substrate of a resin impregnated glass cloth is employed as a matrix, it is difficult to cut off the substrate in the neighborhood of the external form line (mold line) of the molded resin layer. Accordingly, there is such a problem that the external form of a package becomes greatly larger than the external form of the molded resin layer.
That is, when manufacturing a CSP, die bonding and the electrical connection wire bonding of a semiconductor chip is carried out in this order to a wiring substrate having wiring patterns and holes for continuity. Thereafter, a metal mold is put on outside of the semiconductor chip and an epoxy-resin or the like is transfer molded in the metal mold. Thereby, a resin sealed layer (molded resin layer) is formed. Then, after solder bumps or the like are formed as external connecting terminals, in the last, along the mold line, the wiring substrate is cut.
However, in the step of forming the molded resin layer, from a gap between a pushing face of the metal mold and the wiring substrate, the mold resin is forced outside to stick firmly on the wiring substrate, resulting in a burr. The length of the burr reaches even 0.3 to 1.2 mm. That makes difficult to separate the wiring substrate at a portion of the burr. Accordingly, it is required to cut at a position more than the length of the burr apart from the mold line, resulting in a problem that the external form of the package becomes larger by 0.6 to 2.4 mm than that of the molded resin layer.
Further, upon cutting a wiring substrate, though different according to the thickness of the substrate, cutting accuracy of a tool or the like, a large excising margin (cutting margin) is required. Consequently, the demand for smaller size can not be fully satisfied. Further, since the cutting tools wear down rapidly to make necessary complicated management of the tools, in addition, to tend to lead to the poor cutting, the cost reduction was difficult.
The present invention was carried out to solve these problems. An object of the present invention is to provide a semiconductor device that is molded by a molded resin layer, thin, small and highly reliable, and a method of manufacturing efficiently such a semiconductor device.
This invention is disclosed in Japanese Patent Application No. 10-055563 on Mar. 6, 1998, and the entire disclosure thereof is incorporated herein by reference.
The first aspect of the present invention relates to a semiconductor device.
The semiconductor device comprises a wiring substrate having a wiring layer on at least one main face of a substrate composed of a resin impregnated glass cloth, a semiconductor element mounted and assembled on the main face of the wiring substrate, a molded resin layer covering and molding an outside of the semiconductor element, and a plurality of external connecting terminals disposed on the other main face of the wiring substrate. Here, below an external form line of the molded resin layer and between the molded resin layer and the wiring substrate, a protrusion comprising an insulating resin is formed.
The second aspect of the present invention relates to a manufacturing method of a semiconductor device.
The manufacturing method comprises a step of forming a wiring layer on at least one main face of a substrate composed of a resin impregnated glass cloth, a step of forming a protrusion mainly consisting of an insulating resin on a first area on the wiring substrate thereon the wiring layer is formed, a step of mounting and assembling a semiconductor element on an area inside of the first area of the wiring substrate, a step of pressurizing a pushing face of a metal mold against the protrusion formed on the wiring substrate to carry out molding of an insulating resin, thereby forming a molded resin layer outside of the semiconductor element, and a step of forming an external connecting terminal on the other main face of the wiring substrate.
The third aspect of the present invention relates to a manufacturing method of a semiconductor device.
The manufacturing method comprises a step of forming a wiring layer on at least one main face of a substrate composed of a resin impregnated glass cloth, a step of forming a protrusion consisting of an insulating resin on a first area on a wiring substrate thereon the wiring layer is formed, a step of, in the first area of the wiring substrate, cutting leaving a part of the protrusion to form a slit hole, a step of mounting and assembling a semiconductor element on an area inside of the first area of the wiring substrate, a step of pressurizing a pushing face of a metal mold against the protrusion left on the wiring substrate to carry out molding of an insulating resin, thereby forming a molded resin layer outside of the semiconductor element, a step of forming an external connecting terminal on the other main face of the wiring substrate; and a step of, in the wiring substrate thereon the external connecting terminal is formed, cutting between the slit holes to separate an inside molded body.
In the semiconductor device and the manufacturing method thereof of the present invention, as the substrate of the resin impregnated glass cloth, one that is obtained by stacking a prepreg, in which an insulating resin such as an epoxy resin, a BT resin or the like is impregnated, into a glass cloth, and by heating/pressing the same, can be employed. The thickness of such an insulating substrate is preferable to be in the range of from 0.08 to 0.30 mm. Incidentally, the BT resin is an addition polymerized thermosetting resin mainly consisting of bismaleimid and triazine. This resin impregnated substrate is excellent in heat resistance and insulating characteristic, and has a good processing characteristic.
In the present invention, on at least one main face of said resin impregnated substrate, a wiring layer of such as inner leads, a signal line or the like is formed, further, on a predetermined position, via holes for extracting the wiring layer to the other main face is bored. Thus, a wiring substrate is obtained.
Here, the pitch and arrangement of the inner leads are designated according to the pitch and arrangement of electrode terminals of the semiconductor element being assembled. Then, the wiring layer including the inner leads is formed by photo-patterning (photo-etching) a conductive metallic layer such as a copper foil or the like disposed on one surface or both surfaces of the substrate of the resin impregnated substrate. Further, the boring of the via holes can be carried out by boring, with a drill of fine diameter or the like, one in which a plurality of the wiring substrates are stacked.
In the present invention, immediate below the external form line (mold line) of the molded resin layer on the wiring substrate, a protrusion consisting of an insulating resin is formed. Thereby, in the step of forming the molded resin layer, the protrusion is pressed against a pushing face of a metal mold to make an intimate contact and seal a gap between the metal mold and the wiring substrate. As a result of this, the molded resin is prevented from being forced outside of the pushing face of the metal mold.
Thus, the protrusion consisting of the insulating resin formed on the wiring substrate, by making an intimate contact with the pushing face of the metal mold, prevents the molded resin from being forced out. For this, it is necessary for the protrusion to have an enough height and a flat part of sufficient magnitude (area) thereon. The protrusion of enough height and flatness is difficult to be formed in a single layer. Accordingly, in the present invention, the protrusion is preferable to be formed by stacking at least two layers of the resin layers.
Further, in such a protrusion where two or more of the resin layers are stacked, an underlying resin layer is preferable to be a protective layer consisting of an insulating resin formed on the wiring substrate covering the wiring layer. As such a protective layer, there is a solder resist layer which has a function through protection of the wiring layer to prevent short-circuit or the like from occurring. Further, this solder resist layer exists as a strength reinforcement of connecting pads of a ball grid array (BGA) package in which, in order to prevent Ni/Au plating layer from sticking, external connecting terminals of the package are generally replaced by the solder balls.
In the present invention, two or more layers of such a solder resist layer are stacked immediate below the mold line with a predetermined width to form a protrusion projected toward the thickness direction compared with the other area.
More specific, the thickness of one layer of the solder resist layer is preferable to be in the range of from 15 to 40 xcexcm, and the thickness of the protrusion stacked two or more layers is preferable to be in the range of from 30 to 80 xcexcm. In addition, by taking into account the shift of the metal mold and the accuracy of the resist pattern, as to the magnitude of the protrusion due to stacking of two or more layers, the width of the portions inside and outside the mold line is preferable to be disposed to be 100 xcexcm or more, respectively.
Thus, in a structure where two or more of the resin layers (solder resist layer) are stacked to form a protrusion, in addition to being capable of obtaining the sufficient height for the protrusion, due to stacking, the step (the difference in level) on the upper surface is absorbed and alleviated and the protrusion of high flatness can be obtained. That is, the wiring pattern on the insulating substrate being relatively thick such as approximately 18 xcexcm in its thickness, only one solder resist layer is insufficient to absorb the step between the insulating substrate and the wiring pattern, to leave a step on the upper surface of the protrusion. However, upon stacking two of the solder layers to form a protrusion, there can be formed a protrusion that has hardly a gap on the upper surface (3 xcexcm or less), and of high flatness.
Here, two or more of the solder resist layers constituting the protrusion may be the layers of consisting of the same insulating resin, or may be the layers of consisting of different insulating resins. However, the underlying solder resist layer is preferable to be constituted of the same material with the solder resist layer formed inside the mold line to protect the wiring layer or the like, and to be formed by the same coating step. Further, the underlying solder resist layer is preferable to be a photo-setting solder resist layer of excellent patterning accuracy, and the upper solder resist layer stacked thereon is preferable to be a thermosetting solder resist layer of excellent processing characteristic such as cutting characteristic or the like.
In the present invention, as the external connecting terminals formed on the other main face of the wiring substrate thereon the wiring layer or the like is formed, there are bumps of ball shape mainly consisting of, for instance, a solder based on Pb/Sn, the bumps being arranged in grid. Then, the formation of such solder bumps can be carried out by mounting while aligning the solder balls formed on, for instance, a bump arrangement plate on the wiring layer (connecting pad) of the other main face of the wiring substrate, to carry out reflow soldering.
Further, in the present invention, in the area where the protrusion of the wiring substrate is formed, in conformity to the external dimension of a semiconductor device to be manufactured, that is, in conformity to the external form line (mold line) of the molded resin layer being formed in the later step, slit holes for separation can be formed. The shape of the slit hole is preferable to have a shape of a rectangle conformed to the mold line, and to be formed with short connecting portions remained at the four corners. For instance, they can be formed by die cutting with a metal mold.
When such slit holes are formed in the wiring substrate, only by cutting the connecting portions, an inside molded body can be easily separated from the surrounding frame portion. Further, when the slit holes are formed on the wiring substrate, since a marginal length (cutting margin) is hardly required to adopt, the slit holes can be formed on the position of the mold line, resulting in a smaller size of a semiconductor device such as a CSP or the like. Still further, an edge surface of an internal circumference of a slit hole formed by die cutting or the like becomes as it is an edge surface of an external circumference of the wiring substrate. Accordingly, an external edge surface of more smooth than the cutting plane due to the cutting tools or the like can be obtained.